The invention relates to bidirectional power converters. More particularly, the inventions described herein relate to systems and methods for creating bidirectional power converters that may be used to covert power in two different directions.
Power conversion circuitry may be found in virtually every device that requires electricity. The purpose of power conversion circuitry is to transfer electrical power from a power source to a load, typically through certain conditioning and regulation circuitry. A typical application of power conversion circuitry is to convert AC power, provided by a power utility, to a regulated DC voltage suitable for use with consumer electronics. Although power conversion circuits are frequently implemented as stand alone systems, often they are constructed as integrated circuits (ICs) and used in various applications such as communications and computing systems.
One type of commonly used power converter is a DC to DC converter, which changes one DC voltage level to another. A step down or buck converter, for example, provides an efficient way of converting a higher DC voltage to a lower DC voltage, which often is desirable in certain electronic systems. A laptop computer, for example, may have a battery supplying 12 volts DC and a processor which requires 5 volts DC. A step down converter, implemented as an IC with some external components, may be used to convert the 12 volt battery voltage to the 5 volts required by the processor with minimal energy loss.
Another type of DC to DC converter is a step up or boost converter. Such converters are used to increase the voltage supplied from a source to a load. For example, an LED may require 3.3 volts DC to emit light. The LED may be powered by a single 1.5 volt battery through the use of a boost converter which may step up the battery voltage to the level required by the LED. Boost converters are also used to provide the higher voltages needed to power fluorescent lights and cathode ray tubes.
In many instances, consumer electronic devices require the use of both step up and step down voltage converters. A portable communications device such as a cellular telephone or PDA is typically battery powered and has a bright, multi colored display screen. When the portable device, such as a BlackBerry, is operating under battery power, the battery voltage used to drive the display screen is stepped up through a boost converter. However, when the device is plugged into a wall socket and its battery is charging, the battery charging circuitry may rely on a buck converter to step down the voltage, in order to provide the proper charging voltage and increase current which charges the battery more quickly.
Often a PDA or other portable communications device is charged through the use of common interconnection link such as a USB link. A BlackBerry, for example, may use the power provided on the USB connection for both operating power and to charge its battery. In the multi-cell battery case where the battery voltage is greater than the voltage on the USB link, a boost converter is used to regulate the supplied voltage, which is typically set to a value just above the battery voltage in order to minimize power dissipation in the charger and to maintain the supply current within USB specifications.
Interconnection links such as a USB link, typically operate in one of two modes. In a host mode or in a slave mode. When a device such as a PDA is connected to a PC through a USB link, the PC acts as the host and provides control functions that power and manage the USB link. Conversely, the USB port in the PDA operates in the slave mode and needs the PC to provide power and to supervise communications so both devices can communicate with one another.
In some instances, however, the USB link in the PDA or other mobile device does not have the capability to operate in the host mode and drive the USB link. Although the mobile device may have the necessary controller circuitry to supervise USB communications, it does not have the capability to provide the power required to drive the USB link. This may be attributed to the voltage supplied by its battery, which, in multiple cell systems, may be significantly higher than that required by the USB link. This condition, coupled with the inability of the mobile device to convert that voltage to a level suitable to drive the USB link, prevent the mobile device from providing the power required. As a result, if the mobile device is connected to another device which may only operate as a USB slave, such as a memory stick, the mobile device cannot power the USB link, preventing these devices from communicating with one another.
Accordingly, in view of the foregoing, it would be desirable to provide circuitry and methods for bidirectional power conversion that allow mobile and other devices to generate power suitable to support multiple applications.